<p>Further countermeasure support came from Douglas EB-66 aircraft, loaded with chaff and jamming equipment, that were assigned to orbit off the main axis of attack to jam the NVA communications and ground-controlled intercept radars.
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<p>In addition to weather, the defenses and the restraints, there were demanding problems with air traffic control. The few Vietnam targets were in a small geographic area, and could only be approached by a few routes. The combination of weather and the number of aircraft to be handled forced the attack patterns into predictable paths, and the NVA was able to move its defenses accordingly. One attempt to bring some order out of the threat of chaos was the division of North Vietnam into six Route Packages. They began at the DMZ, with RP 1 extending northward, and ended with RP VI, further subdivided into VI-A and VI-B, both reaching to the buffer zone at the Chinese border. RP V and VI-A, in the northwest, were assigned to the USAF; RP VI-A contained Hanoi. The Navy drew RP VI-B, on the coast and containing the port city of Haiphong.
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<p>Rolling Thunder began with about 1,500 tactical sorties during April 1965, flown by USAF and Navy aircraft. That figure rose to almost 4,000 by September, and then fell off in October as the monsoon swept in. The strikes had been heavy, but relatively ineffective.
